I've had a surging idle situation lately and its annoying. Ive changed my IAC, IAT, sparks, wires, coil and egr valve and even before I changed those things my car would idle erratically. A normal idle would be about 600 on my tach (which actually is 100 or so rpm higher then the actual idle). When it surges it'll go all the way up to 1200 on the tach. I hear a loud sucking noise when it does idle up. I have a scanning device that I use to check all of my computer data but I dont know what exactly to look for. I've checked the archives and havent found any useful info. What should I be looking for to determine my surging idle situation? I also have a high rpm miss, if thats related. Thanks in advance-

 

You need to watch MAP to see if the sucking noise represents some sort of vacuum leak. Then you need to watch IAC counts to see how the PCM responds to the vacuum leak, or whatever it is. Also check TPS voltage. If, for some reason it blips above 1.00V, the PCM will increase IAC counts/idle speed, on the assumption the engine is about to accelerate.

Do you have any data at all showing that happens when the idle speed suddenly increases?

 

O.K. I got some useful information this afternoon-
The MAP sensor numbers didnt change they were 10-12 at idle at 118-121 degrees and a little less when it surged.
The IAC counts went through the roof when it surged. It idled at 13-17, then shot all the way up to 37-40 when it would surge.
The TPS voltage at idle stayed at .59 then whole time.
The MAF sensor at idle was 7.3 g/s.
The LTF bank 1 & 2 was 114.
Any suggestions?

 

10-12 whats? kPa? "hg?. 118-121degrees of what? Coolant temp? Inlet air temp?

 

the manifold pressure was measured in "hg and I thought the temperature was the manifold temp, but it was probably the IAT. My car is still hunting at idle from 550 to 1200 rpm and sometimes it dies.

 

Nothing seems unusual with regard to TPS. MAP appears to be a little on the high side... I would expect to see 9.5-10"Hg at idle on a stock cam. Seems odd the PCM is commanding the IAC motor to add air by opening it up from 15 counts to almost 40. But 40 isn't "through the roof". Normal reading would be in the range of 20-40. "Through the roof" would be maybe 50-120.

When you did the idle test data, was the A/C or the defroster on? When the PCM sees the compressor kick on, it increases the IAC count to keep the idle where it is supposed to be. Perhaps your A/C isn't working right and the "sucking" sound is related to that??????

 

I forgot to mention that the idle doesnt act up until the fan turns on, and especially when the ac is cranked up. I checked all of my vacuum lines and everything looked copastetic. What are the odds the sucking sound could be my cold air induction and that my computer is just out of whack?

 

Could it be surging when your A/C compressor kicks on?